Exhaust gas receiver, internal combustion engine and method for selective catalytic reduction

ABSTRACT

An exhaust gas receiver that is connectable to an internal combustion engine for receiving exhaust gases from the engine, the exhaust gas receiver comprising a receiver chamber, at least one exhaust inlet, at least one exhaust outlet, and a reducing agent duct, at least a portion of the reducing agent duct being arranged inside the receiver chamber for heating the reducing agent before the reducing agent is mixed with the exhaust gases. The invention also concerns an internal combustion engine and a method for selective catalytic reduction.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an exhaust gas receiver according tothe preamble of claim 1. The invention also concerns an internalcombustion engine and a method for selective catalytic reduction ofexhaust gases of an internal combustion engine, as defined in thepreambles of the other independent claims.

BACKGROUND OF THE INVENTION

Nitrogen oxide (NOx) emissions of internal combustion engines in shipsand power plants are a growing concern and subject to continuouslytightening regulations set by the International Maritime Organization(IMO) and other legislative bodies. To a certain extent, therequirements set by different regulations can be met by means that aredirectly related to the operation of the engine, such as exhaust gasrecirculation, high fuel injection pressures in diesel engines, waterinjection into the air intake duct etc. However, many engine-relatedmeasures for reducing NOx emissions have a negative effect on the fuelefficiency, and they are not adequate for meeting the most stringentemission limits. For ultimate NOx reduction, selective catalyticreduction (SCR) is needed. With the SCR, NOx reductions of up to 90% oreven greater can be achieved.

In an SCR system a catalyst material and a reducing agent are used todecompose the NOx formed during the combustion back to the basicelements. In a typical SCR system, the catalyst is arranged on thesurface of a supporting ceramic material forming a honeycomb structureinside a reactor. On the surface of the catalyst, the NOx reacts withammonia that is used as the reducing agent and nitrogen and water isformed. In practice, urea is often used instead of ammonia for safetyreasons. This applies especially to the marine applications, whereleaking ammonia is a serious hazard. Urea is injected into the exhaustgas flow in an aqueous solution. Due to the high temperature of theexhaust gas, water evaporates and the urea molecules break up intoammonia and carbon dioxide.

A typical SCR system comprises a urea tank, from which the urea solutionis delivered by means of a pumping unit. A dosing unit is used toprovide the correct urea solution flow rate for injection. The ureasolution is injected into the exhaust gas duct by means of an injectionunit. An often used injection unit type comprises two coaxial pipes, ofwhich the inner one is for the urea solution and the outer one forcompressed air that is mixed with the urea solution in a nozzle to forma fine spray that mixes with the exhaust gas flow. An alternativesolution is to use high-pressure urea injection without air-assisting.

For effective NOx reduction and minimized usage of urea, as well as forminimum ammonia slip through the SCR system, effective mixing of theurea with the exhaust gas flow is essential. In many prior artsolutions, sufficient mixing has been ensured by arranging a relativelylong exhaust duct section between the point of urea injection and thecatalyst elements. However, this sets limitations for the constructionof the exhaust system. Especially in ships, where the available space islimited, it is desirable that the exhaust system requires as littlespace as possible. In addition, if the catalytic converter is placed farfrom the engine, low temperature of the exhaust gases may have anegative effect on the functioning of the catalytic converter.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an improved exhaustgas receiver that facilitates the mixing of reducing agent with exhaustgases of an internal combustion engine. The characterizing features ofthe exhaust gas receiver according to the present invention are given inthe characterizing part of claim 1. Another object of the presentinvention is to provide an improved internal combustion engine and amethod for selective catalytic reduction of exhaust gases of an internalcombustion engine. The characterizing features of the internalcombustion engine and the method according to the present invention aregiven in the characterizing parts of the other independent claims.

According to the present invention, the exhaust gas receiver that isconnectable to an internal combustion engine for receiving exhaust gasesfrom the engine comprises a receiver chamber, at least one exhaustinlet, at least one exhaust outlet, and a reducing agent duct, at leasta portion of the reducing agent duct being arranged inside the receiverchamber for heating the reducing agent before the reducing agent ismixed with the exhaust gases.

According to the present invention, in the method for selectivecatalytic reduction of exhaust gases of an internal combustion engine,reducing agent is mixed with exhaust gases of the engine, and themixture of the reducing agent and the exhaust gases is guided through acatalyst element. Before being mixed with the exhaust gases, thereducing agent is heated in a receiver chamber of an exhaust gasreceiver.

The invention has several advantages. When the reducing agent is heatedin the exhaust gas receiver before being mixed with exhaust gases, goodmixing can be achieved even when the mixing distance is short. The sizeand weight of the SCR system can consequently be substantially reduced.Due to the effective mixing, also the catalyst elements that are usedfor selective catalytic reduction can be arranged before turbochargers.

According to an embodiment of the invention, the exhaust gas receivercomprises means for injecting reducing agent into the exhaust gasreceiver. If the injection nozzles are integrated with the exhaust gasreceiver, a modular structure can be achieved.

According to an embodiment of the invention, the means for injectingreducing agent are arranged to inject the reducing agent into thereceiver chamber.

According to an embodiment of the invention, the means for injectingreducing agent are arranged to inject the reducing agent into theexhaust inlet. If the means for injecting the reducing agent arearranged in the exhaust inlet, the mixing distance can be maximized.

According to an embodiment of the invention, the means for injectingreducing agent are connected to the reducing agent duct with firstconnecting ducts that are arranged inside the exhaust gas receiver. Whenthe first connecting ducts are arranged inside the exhaust gas receiver,heat transfer from the exhaust gases to the reducing agent can beincreased.

According to an embodiment of the invention, the exhaust gas receivercomprises a pressure medium duct supplying pressure medium forfacilitating the injection of the reducing agent, and at least a portionof the pressure medium duct is arranged inside the receiver chamber forheating the pressure medium. By mixing the reducing agent with forinstance pressurized air, the reducing agent mixes even better with theexhaust gases. Heating of the pressurized air helps to vaporize thewater in the reducing agent solution and to break the urea molecules.

According to an embodiment of the invention, the pressure medium duct isconnected to the means for injecting reducing agent with secondconnecting ducts that are arranged inside the exhaust gas receiver. Whenthe second connecting ducts are arranged inside the exhaust gasreceiver, heat transfer from the exhaust gases to the pressure mediumcan be increased.

According to an embodiment of the invention, a mixing chamber isarranged inside the receiver chamber. Inside the mixing chamber, thereducing agent can be mixed with a smaller amount of exhaust gasesbefore being introduced into the receiver chamber.

According to an embodiment of the invention, the mixing chambercomprises apertures opening into the receiver chamber. According toanother embodiment of the invention, the exhaust gas receiver comprisesa fan or compressor for introducing exhaust gas into the mixing chamber.According to another embodiment of the invention, the exhaust gasreceiver comprises means for injecting reducing agent into the mixingchamber. From the mixing chamber, the reducing agent and exhaust gasescan be introduced through the apertures into the receiver chamber by thepressure difference between the chambers. The fan or compressorfacilitates the exhaust gas flow into the mixing chamber and also out ofthe chamber.

According to an embodiment of the invention, a catalyst element isarranged inside the receiver chamber. When the catalyst element isarranged inside the receiver chamber, no separate reactor is needed forthe catalyst elements and a compact SCR arrangement can be achieved. Theselective catalytic reduction can also take place immediately after theengine before any turbocharger.

According to an embodiment of the invention, the exhaust outlet of theexhaust gas receiver is connectable to a turbocharger.

The internal combustion engine according to the present inventioncomprises an exhaust gas receiver defined above, the exhaust gasreceiver being connected to the engine for receiving exhaust gases fromthe engine.

According to an embodiment of the invention, in the method for selectivecatalytic reduction the reducing agent is heated by guiding it through areducing agent duct that is arranged at least partly inside the receiverchamber of the exhaust gas receiver.

According to an embodiment of the invention, the reducing agent isinjected into the exhaust inlets of the exhaust gas receiver.

According to an embodiment of the invention, the reducing agent is mixedwith exhaust gases in a mixing chamber that is arranged inside thereceiver chamber.

According to an embodiment of the invention, the injection of thereducing agent is facilitated by pressure medium, and the pressuremedium is heated in the receiver chamber before being mixed with thereducing agent.

According to an embodiment of the invention, the mixture of the exhaustgases and the reducing agent is guided through a catalyst element thatis arranged inside the receiver chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an internal combustion engine with an exhaust gas receiver.

FIG. 2 shows an exhaust gas receiver according to an embodiment of theinvention.

FIG. 3 shows a partially cross-sectional view of an exhaust gas receiveraccording to another embodiment of the present invention.

FIG. 4 shows a partially cross-sectional view of an exhaust gas receiveraccording to a third embodiment of the invention.

FIG. 5 shows a partially cross-sectional view of an exhaust gas receiveraccording to a fourth embodiment of the invention.

FIG. 6 shows a partially cross-sectional view of an exhaust gas receiveraccording to a fifth embodiment of the invention.

FIG. 7 shows a partially cross-sectional view of an exhaust gas receiveraccording to a sixth embodiment of the invention.

FIG. 8 shows a cross-sectional view of an exhaust gas receiver accordingto a seventh embodiment of the present invention.

FIG. 9 shows a cross-sectional view of an exhaust gas receiver accordingto an eight embodiment of the present invention.

FIG. 10 shows a cross-sectional view of an exhaust gas receiveraccording to a ninth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention are now described in more detailwith reference to the accompanying drawings.

In FIG. 1 is shown an internal combustion engine 14 that is providedwith an exhaust gas receiver 1 for receiving exhaust gases from theengine 14. The exhaust gas receiver 1 is arranged on top of the engine14 so that the longitudinal axis of the exhaust gas receiver 1 isparallel to the longitudinal axis of the engine 14. The engine 14 ofFIG. 1 is a large two-stroke internal combustion engine comprising sevencylinders that are arranged inline. However, the invention is notlimited to two-stroke engines or to engines with a certain cylinderconfiguration or number of cylinders, but can also be applied tofour-stroke engines and for instance to engines where the cylinders arearranged in a V-configuration. Although the invention is particularlyadvantageous when used with ship engines, it can also be applied forinstance to engines that are used at power plants. The engine 14 isprovided with two turbochargers 15 a, 15 b that are connected to exhaustoutlets 4 a, 4 b of the exhaust gas receiver 1. The number of theexhaust outlets 4 and turbochargers 15 can vary for instance based onthe number of cylinders in the engine 14. In FIG. 1 is shown twoturbochargers 15 a, 15 b that are arranged in parallel, but the engine14 could also be provided with two-stage turbocharging, where twoturbo-chargers are arranged in series.

Exhaust gas receivers 1 according to different embodiments of thepresent invention are shown in FIGS. 2-10. The exhaust gas receiver 1comprises an elongated cylindrical receiver chamber 2, exhaust inlets 3and exhaust outlets 4. In the embodiments of the figures, the number ofthe exhaust inlets 3 equals the number of the cylinders of the engine14. However, also other arrangements are possible. Instead of having oneexhaust inlet 3 for each cylinder of the engine 14, the cylinders of theengine 14 could be connected to a common duct that is connected to oneor more exhaust inlet 3 of the exhaust gas receiver 1. Alternatively,for instance in a V-engine, the engine could be provided with oneexhaust gas receiver 1 for each bank of the engine and both exhaust gasreceivers 1 would comprise one exhaust inlet 3 for each cylinder of thecorresponding bank of the engine.

For facilitating the mixing of reducing agent with exhaust gases of theengine 14 before selective catalytic reduction, the reducing agent isheated in the exhaust gas receiver 1 before being mixed with the exhaustgases. The reducing agent can be for instance ammonia that is deliveredin the form of a urea-water solution. For heating the reducing agent,part of a reducing agent duct 5 is arranged inside the receiver chamber2 of the exhaust gas receiver 1. When the reducing agent flows in thereducing agent duct 5 inside the receiver chamber 2, hot exhaust gasesheat the reducing agent. The length of the portion of the reducing agentduct 5 that is inside the receiver chamber 2 is chosen so thatsufficient temperature of the reducing agent is achieved. The neededtemperature depends for instance on the type of the reducing agent andthe distance between the reducing agent injection point and catalystelements. The achieved temperature depends for instance on the flowspeed of the reducing agent and the exhaust gas temperature in thereceiver chamber 2.

The reducing agent is injected into the exhaust gas receiver 1 throughnozzles 8. In the embodiments of FIGS. 2-8, the reducing agent isinjected into the exhaust inlets 3 of the exhaust gas receiver 1. In theembodiment of FIG. 9, the reducing agent is injected into the receiverchamber 2 of the exhaust gas receiver 1. In the embodiment of FIG. 10,the reducing agent is injected into a mixing chamber 9. The mixingchamber 9 is arranged inside the receiver chamber 2 and it is separatedwith a wall 10 from the receiver chamber 2. The mixing chamber 9 couldalso be a separate chamber outside the exhaust gas receiver 1. The wall10 of the mixing chamber 9 is provided with holes 11, through which thereducing agent that is mixed with exhaust gases can be introduced intothe receiver chamber 2. The exhaust gas receiver 1 can be provided witha fan or compressor that is used to introduce exhaust gases into themixing chamber 9. When part of the exhaust gases of the engine 14 areintroduced into the mixing chamber 9 together with the preheatedreducing agent, temperature of the reducing agent is further increased.

To further facilitate the mixing of the reducing agent with the exhaustgases, the reducing agent can be mixed in the nozzles 8 with pressurizedair. The pressurized air is introduced into the nozzles 8 through apressure medium duct 6. Also the pressure medium duct 6 can be arrangedpartly inside the receiver chamber 2 of the exhaust gas receiver 1, asshown in FIGS. 3, 5 and 7-10. The nozzles 8 are connected to thereducing agent duct 5 with a first connecting duct 12 and to thepressure medium duct 6 with a second connecting duct 13. In theembodiments of FIGS. 7-10, each nozzle 8 is connected with its ownconnecting ducts 12, 13 to the reducing agent duct 5 and the pressuremedium duct 6. In the embodiments of FIGS. 2 and 4-6, the nozzles 8 areconnected to a reducing agent distribution duct 16 and to a pressuremedium distribution duct 17. The connecting ducts 12, 13 can be arrangedeither inside the exhaust gas receiver 1, as shown in FIGS. 8-10, or atleast partly outside the exhaust gas receiver 1, as shown in FIG. 7. Ifthe connecting ducts 12, 13 are arranged inside the exhaust gas receiver1, the temperature of the reducing agent and pressurized air can beincreased more than in the arrangement where the connecting ducts 12, 13are outside the receiver chamber 2. The distribution ducts 16, 17 andthe connecting ducts 12, 13 can be insulated if they are arrangedoutside the exhaust gas receiver 1.

In the embodiment of FIG. 3, the reducing agent duct 5 and the pressuremedium duct 6 are connected to a gasifier 18 that is outside the exhaustgas receiver 1. In the gasifier 18, the reducing agent and the pressuremedium are mixed. The pressure medium can be air or some other gas, suchas exhaust gas from the engine 14. From the gasifier 18, the reducingagent and the pressure medium are introduced into a feeding duct 19where the mixture evaporates. The feeding duct 19 is outside the exhaustgas receiver 1 and accommodates the nozzles 8 that are used to injectthe reducing agent into the exhaust inlets 3 of the exhaust gas receiver1. In this embodiment, an insulating layer is arranged around thefeeding duct 19. The feeding duct 19 could also be arranged inside thereceiver chamber 2.

According to an embodiment of the invention, a catalyst element 7 isarranged inside the receiver chamber 2, as can be seen in FIGS. 3-10.With this arrangement, no separate reactor is needed for the catalystelements 7 and the whole SCR process takes place inside the exhaust gasreceiver 1. Alternatively, the catalyst elements 7 can be arranged in aseparate reactor that is located close to the exhaust gas receiver 1.

In the embodiments of FIGS. 4 and 5, the SCR arrangement is providedwith a pumping unit 20 that circulates the reducing agent inside thereceiver chamber 2 keeping it at the optimal temperature. In FIG. 5 isalso shown a control air duct 21 that is used to supply pressurized airfor opening dosing valves that control the injection of the reducingagent.

It will be appreciated by a person skilled in the art that the inventionis not limited to the embodiments described above, but may vary withinthe scope of the appended claims. For instance, features of thedifferent embodiments can be combined.

1. An exhaust gas receiver that is connectable to an internal combustionengine for receiving exhaust gases from the engine, the exhaust gasreceiver comprising a receiver chamber, at least one exhaust inlet, andat least one exhaust outlet, wherein the exhaust gas receiver comprisesa reducing agent duct, and at least a portion of the reducing agent ductis arranged inside the receiver chamber for heating the reducing agentbefore the reducing agent is mixed with the exhaust gases.
 2. Theexhaust gas receiver according to claim 1, wherein the exhaust gasreceiver comprises means for injecting reducing agent into the exhaustgas receiver.
 3. The exhaust gas receiver according to claim 2, whereinthe means for injecting reducing agent are arranged to inject thereducing agent into the receiver chamber.
 4. The exhaust gas receiveraccording to claim 2, wherein the means for injecting reducing agent arearranged to inject the reducing agent into the exhaust inlet.
 5. Theexhaust gas receiver according to claim 3, wherein the means forinjecting reducing agent are connected to the reducing agent duct withfirst connecting ducts that are arranged inside the exhaust gasreceiver.
 6. The exhaust gas receiver according to claim 1, wherein theexhaust gas receiver comprises a pressure medium duct supplying pressuremedium for facilitating the injection of the reducing agent, and atleast a portion of the pressure medium duct is arranged inside thereceiver chamber for heating the pressure medium.
 7. The exhaust gasreceiver according to claim 6, wherein the pressure medium duct isconnected to the means for injecting reducing agent with secondconnecting ducts that are arranged inside the exhaust gas receiver. 8.The exhaust gas receiver according to claim 1, wherein a mixing chamberis arranged inside the receiver chamber.
 9. The exhaust gas receiveraccording to claim 8, wherein the mixing chamber comprises aperturesopening into the receiver chamber.
 10. The exhaust gas receiveraccording to claim 8, wherein the exhaust gas receiver comprises a fanor compressor for introducing exhaust gas into the mixing chamber. 11.The exhaust gas receiver according to claim 8, wherein the exhaust gasreceiver comprises means for injecting reducing agent into the mixingchamber.
 12. The exhaust gas receiver according to claim 1, wherein acatalyst element is arranged inside the receiver chamber.
 13. Theexhaust gas receiver according to claim 1, wherein the exhaust outlet ofthe exhaust gas receiver is connectable to a turbocharger.
 14. Theinternal combustion engine, wherein the engine comprises an exhaust gasreceiver according to claim 1, the exhaust gas receiver being connectedto the engine for receiving exhaust gases from the engine.
 15. A methodfor selective catalytic reduction of exhaust gases of an internalcombustion engine, in which method reducing agent is mixed with exhaustgases of the engine, and the mixture of the reducing agent and theexhaust gases is guided through a catalyst element, wherein the reducingagent is heated in a receiver chamber of an exhaust gas receiver beforebeing mixed with the exhaust gases.
 16. The method according to claim15, wherein the reducing agent is heated by guiding it through areducing agent duct that is arranged at least partly inside the receiverchamber of the exhaust gas receiver.
 17. The method according to claim15, wherein the reducing agent is injected into the exhaust inlets ofthe exhaust gas receiver.
 18. The method according to claim 15, whereinthe reducing agent is mixed with exhaust gases in a mixing chamber thatis arranged inside the receiver chamber.
 19. The method according toclaim 17, wherein the injection of the reducing agent is facilitated bypressure medium, and the pressure medium is heated in the receiverchamber before being mixed with the reducing agent.
 20. The methodaccording to claim 15, wherein the mixture of the exhaust gases and thereducing agent is guided through a catalyst element that is arrangedinside the receiver chamber.